The present invention relates to improvements in Japanese Patent Application No. Hei 3-130840 and more particularly to a wheel-acting force measuring device for measuring forces acting on a wheel, such as a road surface friction force and a road surface friction coefficient, which can be used as a component of either an antilock brake system (ABS) for preventing the locking of wheels on application of the hard brake to the vehicle or a traction control system (TCS) for preventing excessive slippage of wheels during acceleration.
The present applicant has previously proposed, in Japanese Patent Application No. Hei 3-130840, a wheel-acting force measuring device comprising a hole formed in or adjacent an axle, a stress detecting sensor, such as a road surface friction detecting sensor or a road surface friction coefficient detecting sensor, fixedly embedded in said hole directly or through a spacing agent such that said stress detecting sensor is disposed on the stress center axis, the detection signal from said stress detecting sensor being processed in a signal processing circuit composed of a bridge circuit.
With the wheel-acting force measuring device described above, the complicated structure of the axle and vehicle body sometimes causes the stress detecting sensor and sensor segment to deviate from the ideal positions on the stress center axis of the brake torque, resulting in the brake torque (torsional torque) component, in addition to the shearing stress, being mixed in the bridge output of the signal processing circuit.
Therefore, in such case, the correct stresses, such as the road surface friction force and road surface friction coefficient, cannot be detected and hence an antilock brake device or traction control system of high precision cannot be obtained. Thus, it is necessary to eliminate cross talk due to brake torque.